[Illustration: Figure 1.--MODELS OF VARIOUS ELECTROMAGNETIC INSTRUMENTS
created by Schweigger, Poggendorf and Cumming in 1821, made for an
exhibit in the Museum of History and Technology, Smithsonian
Institution. (Smithsonian photo 49493.)]
_The history of the early stages of electromagnetic instrumentation
is traced here through the men who devised the theories and
constructed the instruments._
_Despite the many uses made of voltaic cells after Volta's
announcement of his "pile" invention in 1800, two decades passed
before Oersted discovered the magnetic effects of a voltaic circuit.
As a result of this and within a five-month period, three men,
apparently independently, announced the invention of the "first"
electromagnetic instrument. This article details the merits of their
claims to priority._
THE AUTHOR: _Robert A. Chipman is chairman of the Department of
Electrical Engineering at the University of Toledo in Toledo, Ohio,
and consultant to the Smithsonian Institution._